Canvas background mode for world environment won't display a background

[EamonnMR]

Godot version

v4.0beta3

System information

Lubuntu

Issue description

Using a canvas background in a world environment results in a blank background.
I think the issue stems from the way gd4 handles negative canvas layers. In order to use a canvas as a background in GD3 you'd set it to a negative layer (so it's not drawn on top of the 3d scene) then set the max layer on the environment background to -1. This would result in your canvas being drawn in the background of your 3d scene. In GD4, when you've set the background to canvas, setting a negative max layer results in nothing being drawn, resulting in a hall-of-mirrors effect instead of your background.

This is a problem because it seems to break using a canvas as a background, which would be the intent of the canvasBackground mode for WorldEnvironment.

This appears to be a regression from Godot 3, where this worked.

(Edit: repro'd this in Beta 3, same issue)

Steps to reproduce

Three top level nodes:

• CanvasLayer
  Put some stuff in to draw
  set layer to -1
• WorldEnvironment
  Set background to canvas, max layer -1
• Spatial
  Put in a camera and some 3d stuff to draw

This illustrates the problem.

Minimal reproduction project

canvas_background_example_gd3.zip
canvas_background_example_gd4.zip

[Calinou]

Related to #52467.

[EamonnMR]

It may be the same fix as above, but this presents in a fairly different context (most of the discussion there is about how it breaks 2d) so I think it's worth keeping open as an issue, but that's up to you!

[MaybeAnonymous]

I have the same problem on Godot 4